This report includes work arising from the following clinical protocols: NCT00005011, NCT00056901, NCT00059228, NCT00082043, NCT00100360, NCT00001177, NCT00001259, and NCT00001481 Overlapping co-morbidities between premenstrual dysphoric disorder (PMDD) and postpartum depression (PPD) have led to suggestions that these disorders represent a continuum of vulnerability, risk and shared pathophysiology. These observations have important implications for both the clinical management of women with PMDD (specifically regarding risk counseling) and for research directions. Nonetheless, comorbidity does not necessarily indicate similar pathophysiology, and the comorbidity shared between PMDD and PPD could be uninformative about pathophysiology, analogous to the comorbidity shared between PMDD and non-reproductive depression. We examined the past histories of PPD in a clinic-based sample of women meeting criteria for PMDD. Our data demonstrate that PMDD and PPD do not frequently co-occur, and do not suggest that PMDD and PPD share similar pathophysiology beyond both being ovarian-steroid triggered mood disorders. In our studies we have developed experimental models for the triggering of symptoms in PMDD and PPD that we employ in our efforts to identify the underlying biology of these conditions. In our gonadotropin releasing hormone (GnRH) agonist-induced ovarian suppression studies (henceforth referred to as the Lupron paradigm) we have demonstrated that the change in ovarian steroid level not the absolute level itself is the trigger for affective destabilization in these women. Indeed, in a recently completed study, our findings confirm that the change in ovarian steroids contributes to the onset of negative affective symptoms in women with PMDD. What remains to be determined is why PMDD symptom recurrence is self-limited and symptoms remit despite continuing stable ovarian steroid levels. Presumably some homeostatic mechanism is activated related to either the presence of the negative affective state or the presence of stable levels of ovarian steroids. The latter possibility has been described in rodents, with alterations in GABA-A subunit conformations occurring after increases or decreases in progesterone or its neurosteroid metabolite allopregnanolone, but with conformations returning to normal during stable levels of these hormones. Although the mechanisms underlying the mood destabilizing effects of ovarian steroids in PMDD remain to be better characterized, as does the source of susceptibility to this trigger, our findings provide a new target on which interventions could be focused. Specifically, these data suggest the promise of therapeutic efforts to inhibit the change in steroid levels proximate to ovulation, similar to our findings that blocking the luteal phase increase in allopregnanolone mitigates PMDD symptom onset. In addition to our studies of the behavioral effects of changes in ovarian steroids, we employ methodologies to investigate the underlying substrates of risk that distinguish women with reproductive endocrine-related mood disorders and those who do not experience these conditions. The techniques employed in these studies include neuroimaging studies, metabolomics platforms, and functional genomics studies: First, our neuroimaging studies have identified both a neural substrate of risk in PMDD as well as a brain-region specific response that could underlie the differential behavioral response to ovarian steroids in this condition. Women with PMDD and controls underwent resting state PET studies during each of the three hormone conditions in the Lupron paradigm, and we observed differences in resting regional cerebral blood flow (rCBF) in women with PMDD compared with controls in both the subgenual cingulate (BA25), and medial orbital frontal cortex (mOFC). Higher resting state rCBF in PMDD was present during hypogonadism (when PMDD symptoms are in remission) compared with estradiol or progesterone replacement (when PMDD symptoms are at risk of recurring), whereas no hormone-related changes were observed in controls in either brain region. These data demonstrate for the first time a differential pattern of rCBF within neuroanatomical loci implicated in the process of affective adaptation. Additionally, the fact that the changes in rCBF correspond in time to the hormone state-related changes in symptoms raises the possibility that the changes in rCBF may reflect the altered mood state rather than a direct effect of ovarian steroid hormonal exposure. These data compliment previous findings from our group in which we demonstrated hormone-independent (i.e., traits) abnormalities in prefrontal recruitment, (i.e., greater activation than controls throughout the dorsolateral prefrontal cortex bilaterally) in PMDD which also correlated with PMDD symptom severity, functional impairment and duration of PMDD. Second, we examined the possibility that women with PMDD metabolize steroids differently than asymptomatic controls and, therefore, produce a different profile of neuroactive steroid metabolites that contributes to the onset of PMDD symptoms. Pharmacometabolomic studies (employing liquid chromatography-tandem mass spectroscopy) are performed in women with PMDD who respond to Lupron with elimination of symptoms and who experience return of symptoms during progesterone (P) or estradiol (E) replacement, as well as controls who experience no change in mood during the identical experimental paradigm. No differences between PMDD and controls were observed in levels of metabolites during Lupron. Importantly, no differences in the formation of P-derived neurosteroids were observed in this otherwise highly selected sample of women studied under controlled hormone. However, despite identical exposures to E and P, women with PMDD were distinguished by differences in their profiles of sulfated steroid metabolites. Relative to the Lupron condition (i.e., suppressed steroid secretion), women with PMDD were distinguished from controls by a significantly attenuated increase in E-3-sulfate, decreases in both DHEA-sulfate and pregnenolone-sulfate after E, and a decrease in DHEA-sulfate after P (compared to an increase in controls). Thus, alterations of sulfotransferase activity could contribute to the differential steroid sensitivity in PMDD. Finally, in collaboration with David Goldman's laboratory (NIAAA), we employ lymphoblastoid cells obtained from women with PMDD and controls who participate in our Lupron studies. In this study, lymphoblastoid cell cultures (LCLs) from women with PMDD and asymptomatic controls were compared via whole transcriptome RNA-seq at baseline and following hormone treatment. As reported previously, women with PMDD manifested ovarian steroid-triggered behavioral sensitivity during a hormone suppression and add-back clinical trial, and controls did not. Pathway analysis of the LCL transcriptome revealed over-expression of ESC/E(Z) complex genes (an ovarian steroid-regulated gene silencing complex) in PMDD LCLs at baseline, with more than half of these genes over-expressed compared to controls. RNA and protein expression of the 13 ESC/E(Z) complex genes were individually quantitated. Finally, mRNA expression of several ESC/E(Z) complex genes were increased by progesterone in controls only, and decreased by estradiol in PMDD LCLs. Our findings provide the first evidence of a plausible biological substrate for the differential behavioral response to E/P in women with PMDD. These findings add further weight to PMDD as a biologically distinct form of affective disorder, as recognized recently in the DSM V. Further clarification of the role of the ESC/E(Z) complex in PMDD and other reproductive endocrine-related mood disorders could identify substrates of risk and targets for intervention, in these conditions.